# Deceleration distance over time

• Plebian
In summary: I can't use it at all.In summary, the conversation discusses the calculation of the distance traveled by a car in 20 seconds with an initial velocity of 20m/s and a deceleration of 5m/s^2. The correct formula for calculating this distance is given and it is noted that the initial formula used did not take into account the fact that the car would eventually come to a stop.
Plebian

## Homework Statement

:
[/B]
A person drives a car for 20 seconds in a straight line with an initial velocity of 20m/s. During the entire course of the journey they applied breaks causing the car to decelerate at 5m/s2. How far will it be from the starting point after the given time?

## Homework Equations

:[/B]
distance = 20 * 20 + 0.5 * -5m/s^2 * 20^2

## The Attempt at a Solution

: [/B]
However since I acquire a negative value, I'm convinced that my working is incorrect. What am I misunderstanding about the deceleration?

Last edited by a moderator:
Hello Plebian,

So what happens to the speed of the car ? As a function of time I mean.

I forgot to mention that I attempted the deceleration over time 20 * 20 + 0.5 * -5m/s^2 * 20 this rendered a better result that looks like it could be correct. I am on the correct track here?

No ! it's not as if you can solve this by trial and error juggling the expressions. The dimensions don't even fit.
Now read post #2 and react to it: what happens if you slam the brakes while moving at 20 m/s and thus reduce your speed with 5 m/s per second ?

BvU said:
No ! it's not as if you can solve this by trial and error juggling the expressions. The dimensions don't even fit.
Now read post #2 and react to it: what happens if you slam the brakes while moving at 20 m/s and thus reduce your speed with 5 m/s per second ?
The velocity of 20m/s would slow down by 5m/s per second.

Yes, that's what I wrote. So after 1 second your speed is .., after 2 ..., after 3 ... and after 4 it is zero. Would it then go negative if you keep braking ?

BvU said:
Yes, that's what I wrote. So after 1 second your speed is .., after 2 ..., after 3 ... and after 4 it is zero. Would it then go negative if you keep braking ?
It would remain stationary at that point.

Does the expression you use in post #1 reflect that ?

BvU said:
Does the expression you use in post #1 reflect that ?
Not at all, which was why I initially posted this query.

So for how long can you use that expression ?

BvU said:
So for how long can you use that expression ?
Point taken.

## 1. What is deceleration distance over time?

Deceleration distance over time refers to the distance covered by an object as it slows down or decreases its speed over a specific period of time.

## 2. How is deceleration distance over time calculated?

Deceleration distance over time can be calculated using the formula: d = (v2-u2)/2a, where d is the distance, v is the final velocity, u is the initial velocity, and a is the deceleration or negative acceleration.

## 3. What factors affect deceleration distance over time?

The main factors that affect deceleration distance over time include the initial speed of the object, the magnitude of deceleration, and the duration of deceleration.

## 4. How does deceleration distance over time differ from acceleration distance over time?

Deceleration distance over time is the distance covered by an object as it slows down, while acceleration distance over time is the distance covered by an object as it speeds up. Additionally, the sign of the acceleration (positive for acceleration and negative for deceleration) is used in the formula to calculate the distance over time.

## 5. Why is understanding deceleration distance over time important in science?

Understanding deceleration distance over time is important in science because it helps us analyze and predict the motion of objects. This is particularly useful in fields such as physics and engineering, where the movement of objects is studied and applied in various real-world situations.

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